Representation of two- and three-dimensional objects by tree structures has been extensively used in solid modeling, computer graphics, computer vision and image processing. More particularly, quadtrees, which are used to represent objects in two-dimensional space, and octrees, which are the extension of quadtrees into three-dimensional space, have been studied thoroughly for applications in graphics and image processing. However, quadtree- and octree-based image representations are rigid and inflexible. For example, an image represented by a quadtree can only be rotated through angles which are multiples of 90 degrees. Also, such tree structures tend to be very deep when used to represent complex images and, therefore, a large number of bits are required to represent the image.